Various window panes for use in motor vehicles have been proposed to date, one example of which is disclosed, for example, in Japanese Patent Laid-Open Publication No. SHO-62-273115 entitled “APPARATUS FOR GUIDING ASCENDING/DESCENDING MOVEMENTS OF AUTOMOBILE WINDOW PANE”. The window pane disclosed in this publication is a curved pane. Although not specifically stated in the publication, the disclosed window pane is arcuately curved so as to form part of a cylindrical surface with its portion parallel to a longitudinal axis of the motor vehicle running linearly or substantially linearly. Namely, the disclosed window pane, i.e., “cylindrically-curved window pane”, has an arcuately-curved vertical section as viewed from the front of the motor vehicle and a near-linear horizontal or lateral section as viewed from above the motor vehicle. However, an overall aesthetic appeal of the motor vehicle would be significantly improved if the window pane is arcuately curved in the lateral section as well as in the vertical section.
Demand for an improved aesthetic appeal may be met by forming the window pane into a spherically curved shape; that is, the spherically curved shape provides an arcuately-curved lateral section as well as an arcuately-curved vertical section. Because of the nature of the spherically curved shape, each and every section taken through the window pane has one and the same radius of curvature. However, for almost every vehicle window pane used today, it is necessary that the vertical section be curved relatively greatly (with a relatively small radius of curvature) toward a roof of the motor vehicle and that the lateral section be slightly curved or be almost like a straight line. Therefore, the spherically-curved window pane, which has a uniform curvature in all directions thereof, particularly, in the directions parallel to and transverse to the longitudinal axis of the motor vehicle, can not readily be put into practical use.
Another type of curved vehicle window pane, analogous in shape to the above-mentioned spherically-curved vehicle window, is proposed, for example, in Japanese Patent Laid-Open Publication No. HEI-11-500796 (International Publication No. WO 96/25580) entitled “GUIDE FOR A LOWERABLE SPHERICALLY CURVED WINDOW PANE IN A VEHICLE DOOR”. More specifically, the publication discloses a vehicle window pane that is curved to form part of an imaginary barrel-shaped envelope surface (hereinafter referred to simply as a “barrel-shaped window pane”), as shown in FIG. 23 hereof.
Specifically, part (a) of FIG. 23 is a side view of the barrel-shaped window pane disclosed in the Japanese Patent Laid-Open Publication No. HEI-11-500796, while part (b) of FIG. 23 shows vertical sections of the disclosed vehicle door window pane taken along lines 31—31, 32—32 and 33—33 of part (a). Because of the barrel shape, the vertical section taken along line 31—31, which is closest to the center of the pane, has a greatest radius of curvature. The vertical section taken along line 32—32, which is farther from the center of the pane than the line 31—31, has a smaller radius of curvature. The vertical section taken along line 33—33, which is still farther from the center of the pane than the line 31—31, has a yet smaller radius of curvature. That is, the farther from the center of the pane, the smaller becomes the radius of curvature of the vertical section. Namely, where the radius of curvature of the line 31—31 vertical section is given as “R31”, the radius of curvature of the line 32—32 vertical section as “R32”, R32<R31. Again, where the radius of curvature of the line 33—33 vertical section is given as “R33”, R33<R32.
Such a barrel-shaped window pane, which progressively varies in the radius of curvature along the horizontal axis or X-axis as shown, would require a complicated shape in guide rails that serve to guide the window pane relative to the door body, as well as a complicated construction in the door body accommodating the window pane. As a consequence, the manufacturing costs of the guide rails and door body will increase, thereby presenting a bar to practical use of the barrel-shaped window pane.
The cylindrically-curved window pane, as typically disclosed in Japanese Patent Laid-Open Publication No. SHO-62-273115, has a drawback of insufficient aesthetic appeal, although it has been popularly used as a sliding vehicle window pane. The spherically-curved and barrel-shaped window panes, on the other hand, have the disadvantage that they are not suitable for practical use.
There has also been a demand for a glass sheet which has a compound curvature and is superior in aesthetic appeal to the above-described spherically-curved and barrel-shaped glass sheets.
An example technique to meet such a demand is disclosed in Japanese Patent Publication No. SHO-49-10331 entitled “METHOD FOR BENDING A GLASS SHEET”. In this method, a glass sheet, held at a deformation temperature, is fed along an elongated path of travel on a gas support bed. The path of travel is bent both transversely and longitudinally in an up-and-down direction or vertically. As a result, the glass sheet is bent to have a compound curvature composed of curves extending both transversely and longitudinally of the sheet. Finally, the glass sheet is quenched to keep that compound curvature. However, in the disclosed technique, since the glass sheet is bent while it is floated by gaseous support means, it is quite difficult to provide the glass sheet with as many curves as desired, with precision. Stated otherwise, because it is bent while it is gas-supported, using a bed of a configuration copied from part of a rotary (e.g., a cylinder and a barrel) or a sphere, the glass sheet is provided with only curves of poor precision which extend transversely and longitudinally thereof at different radii of curvature.
Another similar technique is proposed in Japanese Patent Laid-Open Publication No. HEI-5-9037 entitled “METHOD AND APPARATUS FOR BENDING A GLASS SHEET”. The proposed technique provides a glass sheet bent with a compound curvature. That is, the glass sheet is bent transversely and longitudinally at different radii of curvature while it is fed along a hearth bed. During feed of the glass sheet, a gas is blown from below the hearth bed to support the glass sheet in a floated fashion. Thus, the proposed technique can provide the glass sheet with only curves of poor precision extending transversely and longitudinally at two different radii of curvature.